1. Field of the Invention
The invention relates to a press tool and a method for connecting by cold forming. Such press tools are also known as press chains, press loops or press rings and are used in particular for connecting pipe sections. For this purpose, the pipe ends to be connected are pushed into a deformable sleeve, a so-called press fitting. For connecting by cold forming, the press jaws are first placed around the press fitting in the manner of a collar that remains open in one area, the two chain ends of the press tool being opposite one another across the open area. The introduction of the drive forces causes the two chain ends to be drawn together. Consequently, the insides of the press jaws are moved together as far as they will go to form an annular press space, and the cold-forming forces are transmitted to the press fitting. To ensure radial cold forming of the fittings that is as uniform as possible, at least three press jaws, generally arranged in the manner of a chain, are typically used for connecting pipes with a diameter greater than 54 mm by cold forming.
2. Description of Related Art
European patent EP627,273 describes a press tool comprising more than two press jaws that are partially movable in a connecting link guide in the circumferential direction. As a result, the press jaws are arranged uniformly over the circumference of the press fitting, which thus permits a uniform radial distribution of the forming forces and prevents flash formation between the press members.
As described in EP627,273, press tools for cold-formed pipe connections having relatively large external cross-sectional diameters, in particular for pipe systems with high internal pressure stresses, require more than two press jaws. More than two press jaws help prevent xe2x80x9crun-outxe2x80x9d of the press fittings or formation of a flash between the end faces of the press jaws on closing the press tool. Run-out of the fittings or formation of a flash makes complete closing and consequently reliable connection impossible.
Such press tools are described, for example, in German Patent DE4,240,427 and European Patent EP922,537. Such tools also available in so-called self-holding versions, which move together even before the introduction of the drive forces. Such tools move together prior to the introduction of the drive forces by pretensioning forces exerted by spring elements. These tools, therefore, need not be additionally held on the workpiece, for example with a hand, to prevent slipping or falling down from the connecting point.
It is an object of the present invention to provide a press tool that is easy to handle, has a simple design and can be used flexibly. The present invention also includes a method for connecting, by cold-forming, workpieces that are inserted one into the other. The method of the present invention permits safe and reliable connection of workpieces having relatively large external cross-sectional shapes and facilitates connections with relatively extensive cold forming. Such press tools should preferably be capable of being used even where there is limited space and should, if necessary, surround, in a nonfrictional manner, the workpieces to be connected.
A press tool according to the present invention is preferably formed with at least two arms, the press jaws advantageously also being used for transmitting the drive forces introduced. The press jaws must be capable of being moved toward one another, the connection of ends of the press jaws by means of bearing bolts having proven a simple and reliable connection concept in terms of design.
The cold-forming forces exerted by the press jaws on the workpieces are initiated by drive forces introduced into the tool. For the introduction of drive forces, engagement regions such as recesses, holes, projections, eyes, hooks, etc. should be provided in at least one area of the press tool. These can be provided at the non-bearing ends of press jaws for application of a drive means that can be optionally coupled.
When, for example, optionally tubular workpieces having predetermined, in particular circular, external cross-sectional shapes are mentioned, it is always to be understood as meaning workpieces having connection regions formed in this manner.
A press tool according to the present invention preferably exerts the cold-forming forces via the insides of the press jaws on the workpieces in a manner such that, when the press jaws move toward one another, xe2x80x9crun-outxe2x80x9d of the outer workpiece and thus the formation of a flash between the press jaws are substantially prevented. To prevent the ends of the inside edges of the press jaws from cutting into the workpiece thus causing the formation of flash, widening recesses in the form of bevels angled outward (i.e., widening toward the end faces) are provided at least on one side (optionally on both, sides) in those regions of the insides of the press jaws that are adjacent to the end faces. The insides of the press jaws may be both angled outward toward the end inside edges and may also be convex. Optionally, the insides of the press jaws may be gradually increasingly curved toward the inside edges, turning outward. The optionally angled insides of the press jaws beveled outward may be in the form of insertion bevels adjacent to the end inside edges. These angled insertion bevels are preferably flat but may also be slightly concave, depending on the machining. If the insertion bevels are slightly. concave, their curvature is less pronounced than that of the remaining inside of the press. jaw. In particular, the insertion bevels have a curvature that is less pronounced than that of a lateral surface segment of a rotational body, and optionally also smaller than the external cross-sectional diameter of the outer workpiece before the cold forming. The curvature of the inside regions of the press jaws adjacent to the inside of the insertion bevels at least approximately corresponds to the remaining external cross-sectional diameter of the cold-formed workpiece.
As a result of these features, the insertion bevels of the insides of the press jaws are shaped at their end inside edges in such a way that, when placed on the workpiece, the insides do not rest on the end inside edges but lie on the outer lateral surface of the workpiece with their inside surface, optionally tangentially, optionally a distance away from the end inside edges.
The extent of the outward angling of the outer end inside regions depends on the external cross-sectional diameter of the respective workpieces coordinated with the press tool. In the case of external cross-sectional diameters between 54 mm and 108 mm, the insertion bevels may be angled, for example, at an angle of 5 to 250 degrees outward relative to the lateral surface directly adjacent to it.
At least two press jaws are required for the operation of a press tool according to the invention. The two press jaws can be mounted around a common bearing bolt, the bearing bolt optionally being eccentric. An eccentric bearing bolt results in those end faces of the press jaws that are not on the bearing side experiencing an additional translational movement apart when the press tool is opened. Consequently, the required opening angle for surrounding the workpieces and the spacing of the end faces in the initially clamped state of the tool can be reduced.
The two press jaws can also each be individually mounted by means of two bearing bolts held in a bearing holder. Once again, at least one bearing bolt can optionally be eccentric. The two bearing bolts can be mounted in the bearing holder both rigidly and coupled to one another. For example, it is possible to provide for each bearing bolt, for relative displacement in the bearing holder, a guide slot along which the bearing bolts are displaceable, and optionally the bearing bolt can be connected via a guide rod system.
The eccentric formation of the bearing bolts and the individual mounting of the press jaws are also suitable for those embodiments in which the insides of the press jaws do not have lateral surface segments of rotational bodies, i.e., the press tool in the closed state encloses a polygonal or oval space instead of an annular space.
To facilitate the placing of the press tool around the workpieces to be connected, and in particular to prevent said press tool from falling down before the mounting of a drive means that can be optionally coupled, it is advantageous to provide the press tool with means that exert pretensioning forces in the closing direction. At least one means exerting pretensioning forces in the closing direction is required for the self-holding operation of a press tool. Said means can be arranged both between the individual press jaws and/or can pass around the press tool in the manner of a clamp open on one side.
Because, on the one hand, the means exerting the pretensioning forces must firmly clamp the press tool onto the workpieces in a non-slip manner and, on the other hand, the press tool should nevertheless be easy to open and to place around the workpieces, means exerting pretensioning forces that have relatively large spring travels are advantageous. This favors coil springs over leaf springs or bar springs, especially in the case of press tools in which the opening of the tool requires large relative movements of few parts. Suitable means exerting pretensioning forces are in principle various components of different, elastically deformable materials. Metallic springs are preferred, but means comprising rubber-like materials, such as tensioning bands or extensible plastics, are also possible. They can be mounted between the press jaws and/or around these, on the outside. Coil springs that are wound around bearing bolts and whose spring ends each exert pretensioning forces on a press jaw permit simple design solutions in combination with convenient handling.
The shape of the insides of the press jaws of the press tool is not limited to lateral surface segments of rotational bodies having identical radii of curvature. If the workpieces are not rotationally symmetrical in the connection region but, for example, have an ellipsoidal, polygonal or irregular shape, or if it is to be converted into such a shape, other embodiments of the insides that are correspondingly adapted to the external cross-sectional shape of the workpieces are possible.
To assist the positioning and guidance of the press tool on workpieces, it is also possible for protuberances and/or recesses, such as, for example, notches or grooves, to be arranged on the insides of the press jaws optionally around the entire inside.
Because the press jaws can have a very narrow design and can be substantially freely pivotable about their bearing bolts, the press tool according to the invention is not only simple and easy to place around workpieces but is also particularly suitable where space is limited, for example in the case of installations in walls and ceilings and in corners.
An inventive, cold-forming connection method for two workpieces pushed partly one into the other and having a predetermined, in particular circular, external cross-sectional shape takes into account the given manufacturing tolerances of the workpieces to be connected in the connection region. Because of the tolerances of the fittings, sockets and pipes, especially in the case of the large nominal connection diameters ND (50 to 100 mm), the required drive forces for moving together the press jaws of a press tool of the prior art to give a closed press space can vary considerably. Consequently, the drive apparatuses and tools have been dimensioned according to the maximum forces occurring. In contrast, the insides of the press jaws of a press tool according to the present invention are formed in such a way that a reliable cold-forming connection is reliably achieved on reaching a predetermined force, even when a tool is not closed. In cooperation with a drive apparatus that can apply specifically predetermined drive forces to the tool for the respective connection processes, controlled connections by means of lighter and more flexible tools and drive apparatuses are possible.